An object of the present invention is to provide improved filter elements while maintaining their advantages, specifically high operating reliability and high beta value stability, even at high flow rates on the medium to be filtered such that especially in operation of the filter element no potential differences can occur between parts of the filter element leading to electrostatic discharges.
This object is basically achieved by a filter element where at least one of the end caps and/or at least one end area of the filter medium has a contact-making means and/or the respective end cap itself or parts of it are made dissipative. For purposes of dissipating the electrostatic charges occurring especially in filter element operation by the fluid medium, it is ensured that the charge generated by triboelectric effects on the filter medium (mesh pack) can drain by contact-making means or the respective end cap to a ground point, for example, formed from metallic housing parts in which the filter element can be held with formation of a filter device. As a result of this dissipation, voltage peaks within the filter element are avoided, with their adverse result that spark discharges can occur which could damage the filter element itself.
In one preferred embodiment of the filter element of the present invention, the contact-making means comprises conductive contact elements which penetrate a cement bed (epoxy resin cement) forming a type of insulating layer between the end cap and the end area of the filter medium accommodated by this end cap to come into dissipative contact with the filter medium. Preferably, the conductive contact elements are contact pins making contact with the mesh pack with their one free end in the cement bed and in the area of the other free end standing vertically upright on the respective end cap. With this solution, the insulating layer of the cement bed is bridged by contact elements in the form of contact pins, with the pins being dimensioned such that in any case the thickness of the cement bed and production tolerances for the filter medium (mesh pack) for dissipating the charge potential are reliably penetrated. The charge prevailing in the filter medium can then drain by this end cap to the housing as the ground point via the dissipative pins preferably injected together with the O-ring-shaped cap as the end cap of the filter medium. Breakdown of the charge with spark formation within the element is then reliably prevented.
In another preferred embodiment of the filter element of the present invention, plastics with a conductivity additive, conductive coatings, or intrinsically conductive plastics are used to form the dissipative end cap or its parts. High quality steel fibers, aluminum flakes, metal-coated glass fibers, or carbon fibers including conductive carbon black are especially well suited as conductivity additives for filled plastics. Dissipative coatings can be applied galvanically or by high vacuum vapor deposition, by painting with conductive enamel or by flame, arc or plasma spaying. Furthermore, the application of nanolayers is conceivable here. Intrinsically conducting polymers (ICP) are plastics in which conductivity is achieved by doping. Plastics suitable for this purpose are especially polyacetylene, polypyrrole, polythiophene and polyaniline.
In another preferred embodiment of the filter element of the present invention, the respective end cap has annular surfaces projecting to the inside and outside, between which the assignable end area of the filter medium fits. The annular surfaces accommodate the contact-making means not only between themselves, but are also used as a lateral stop for the cement as soon as it is added to the end cap for a connecting process.
In another preferred embodiment of the filter element of the present invention, at least that end cap with the contact-making means has a connecting part for fixing the filter element in a filter housing and a sealing means, especially in the form of an O-ring located between the filter housing and the end cap of the filter element, made dissipative. Due to the dissipative O-ring the filter element with its front surface need not necessarily be pressed against the housing surrounding the filter element to produce the necessary dissipative contact. Rather, in addition or alternatively, a version of the filter element can be conceivable with a dissipative O-ring to discharge the potential difference.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.